Seismology is used for exploration, archaeological studies, and engineering projects that require geological information. Exploration seismology provides data that, when used in conjunction with other available geophysical, borehole, and geological data, can provide information about the structure and distribution of rock types and their contents. Such information greatly aids searches for water, geothermal reservoirs, and mineral deposits such as hydrocarbons and ores. Most oil companies rely on exploration seismology to select sites in which to drill exploratory oil wells.
Traditional seismology employs artificially generated seismic waves to map subsurface structures. The seismic waves propagate from a source down into the earth and reflect from boundaries between subsurface structures. Surface receivers detect and record reflected seismic waves for later analysis. Though some large-scale structures can often be perceived from a direct examination of the recorded signals, the recorded signals must be processed to remove distortion and reveal finer detail in the subsurface image.
Typically, the recorded signals from each shot (i.e., each firing of the source) are processed to form a depth-based partial image of the subsurface. These partial images generally have a large degree of overlap with each other, providing significant redundancy and an opportunity to improve the image's signal-to-noise ratio by “stacking” the partial images. Stacking traditionally means averaging the partial image values where they overlap. The noise is generally uncorrelated from partial image to partial image, so the averaging operations usually causes the noise to cancel out, particularly where each portion of the final image may be derived from an average of ten or more partial images. In many cases, however, the final image still has an undesirable amount of residual noise.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure, but on the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed with the given embodiments by the scope of the appended claims.